Biological semiconductors (BSC) are electronic components that change conductivity based upon biological interactions, such as protein-protein interactions, DNA-protein binding, nucleic acid binding, and hormone-receptor binding. The ability to directly measure such biological interactions has scientific, medical, and industrial applicability.
Nanomaterials are increasingly being adapted for biosensing. Once such nanomaterial can be fabricated using single-walled carbon nanotubes (SWNT). The SWNTs are molecular wires with unique electrical properties attractive for solid-state nanoelectronics including logic gates, digital memory, digital switching and integration into logic circuits transistor arrays. Individual SWNTs are quantum wires so their conductivity depends on how conduction electrons interact with the atoms within the SWNTs. The electrical conductance of a single nanotube was shown to be highly sensitive to its environment, and varies significantly with changes in electrostatic charges and surface adsorption of many molecules. Using chemical vapor deposition (CVD) to grow individual tubes, it was shown that there is a large conductance change in response to the electrostatic, chemical and biological molecules when they are utilized as gates for field-effect transistors (FETs) chemical and biological sensors. In addition to this semiconductor effect for an individual tube, SWNTs interconnected in a submonolayer network (also fabricated by CVD) were shown to exhibit semiconductor-like behavior in which the conductance can be gated and surface interactions with biomolecules can be used for biosensing.
Unfortunately, the method of FET fabrication using individual or submonolayer networks of SWNTs is complex and requires on-chip SWNTs synthesis for each FET, making it particularly difficult for fabricating multi-FET chips. Additionally, CVD fabrication is expensive and requires special expertise. For these reasons, fabricating FETs using SWNTs has been very limited.
It is desirable, therefore, to provide a biological semiconductor that is relatively simple to fabricate (especially for multi-gate devices) and can be made at low cost.